The invention relates to improvements in motor vehicles, and more particularly to improvements in power trains which can be utilized in passenger cars, trucks, vans and/or other types of motor vehicles. Still more particularly, the invention relates to improvements in power trains of the type having an automated torque transmitting system (hereinafter often called clutch or friction clutch for short) between a prime mover (such as an engine or a motor) and a transmission or downstream of the transmission. The invention also relates to improvements in methods of and in means for operating an automated clutch in the power train of a motor vehicle.
It is known to provide a power train with a signal receiving, processing and transmitting control unit which can influence the condition (such as the extent of engagement or disengagement) of an automated clutch by way of one or more actuators. As used in this specification, the term "actuator" denotes or can denote a device that performs an action or outputs a signal in response to a signal from a computer, such as from the electronic circuit of a signal receiving, processing and transmitting control unit. For example, the control unit can receive signals from one or more sensors and/or electronic circuits by way of one or more buses and/or other types of signal transmitting conductors, and comprises an electronic circuit (such as a microprocessor) which transmits processed or evaluated signals to one or more actuators serving to partially or fully engage or disengage the automated clutch by way of a fluid-operated, mechanical and/or other clutch engaging/disengaging arrangement. The signals which are being transmitted to the electronic circuit of the control unit can be processed to indicate the extent of slip between the customary friction linings of a rotary clutch plate or clutch disc and the adjacent (engine-driven) constituent(s) of the automated clutch. Signals denoting the thus determined slip and hence the magnitude of the torque which the clutch can transmit can be utilized to ascertain the energy input in the region of the friction linings, to determine the rise of the temperature of the friction linings in comparison with a preselectable value, and/or the extent of wear upon the friction linings.
Motor vehicles with power trains of the above outlined character are disclosed, for example, in published German patent applications Nos. 40 11 850 (corresponding to U.S. Pat. No. 5,176,234) and 196 02 006 (corresponding to U.S. Pat. No. 5,823,912). A drawback of conventional power trains is that improper utilization of the automated clutch can lead to accidents and/or extensive damage to the power train. For example, if a motor vehicle is to be brought to a halt on an inclined road surface without the utilization of the vehicle brake, or when an attempt is made to start the vehicle while the transmission is in a gear other than a gear which is suitable for starting, this involves an increased energy input in the region of the friction linings on the clutch disc or clutch plate of the friction clutch due to an increased slip between the friction linings and the adjacent constituents (such as an engine-driven flywheel and an engine-driven spring-biased pressure plate of the clutch). Any increase of slip entails an undesirable pronounced rise of temperature which, in turn, can contribute to a greatly increased wear upon, or even to a destruction of, the friction linings.
The power train which is disclosed in the aforementioned published German patent application No. 40 11 850 (corresponding to U.S. Pat. No. 5,176,234) is constructed and assembled in such a way that the clutch is automatically engaged or disengaged when the frictional capability or engagement of the clutch reaches a preselected value. For example, if the power train happens to disengage its automated clutch without any prior warning or signaling to the operator of the motor vehicle, the power flow from the prime mover (such as a motor or an internal combustion engine) to the driven wheels is interrupted, i.e., the operator is no longer in a position to accelerate the vehicle. This can entail serious danger to the occupant(s) of the motor vehicle, e.g., when the vehicle is at a standstill and an accident and/or another calamity can develop if the motor vehicle cannot be set in motion or cannot be set in motion within a relatively short or very short interval of time. Automatic engagement of the clutch without prior notice, signal or any other warning to the operator of the motor vehicle can also result in or lead to situations which are or which might be dangerous to the occupant(s) and/or can be a cause of damage to or complete destruction of the motor vehicle.
The power trains which are disclosed in the aforementioned published German patent application No. 196 02 006 (corresponding to U.S. Pat. No. 5,823,912) are designed in such a way that the operator of the motor vehicle is warned, for example, when the temperature of the friction linings rises to an undesirable predetermined value and/or when the wear upon the friction linings forming part of an automated friction clutch exceeds a preselected maximum permissible wear. For example, the warning or notice can consist in that the automated friction clutch is caused to transmit a torque which varies as a function of time and entails a jolting or bucking or analogous undesirable (because uncomfortable) movements of the motor vehicle. Such variations of torque, which is being transmitted by the automated clutch in response to excessive wear upon and/or an overheating of the friction linings, persist if the operator fails to detect and/or to react to the bucking and/or other undesirable irreguar movements of the vehicle. This, in turn, can entail an overheating of the clutch actuating or operating means and can result in damages which are caused by such overheating.